As an example of a medical field, description is made by taking orthodontics as an example.
In the orthodontics, medical treatment of malocclusion, for example, improvements of so-called projecting teeth, a mouth with a protruding lower lip, a teeth arrangement is provided. However, the treatment is not for merely regularly arranging teeth. For example, a teeth arrangement and occlusion of an anterior tooth portion are deeply related to aesthetic properties of a mouth and a complexion. The occlusion is constituted by a pair of maxillary dentition and mandibular dentition. In order to obtain good results of treatment by both the occlusion and the complexion, therefore, the position of teeth in a maxilla and a mandible, the deviation between the maxilla and the mandible, and the positional relationship of the mandible in a skull, and so forth must be sufficiently considered to provide treatment.
Cephalometrics films which have been introduced from about 1940 are frequently used as indispensable examination materials for obtaining a lot of information relating to teeth, a maxilla, a mandible and a skull in a clinical study of the orthodontics even at the present time.
Anatomical measuring points (landmarks) on bones are common among human beings, and are widely used in knowing the difference in a skeletal form between races and respective skeletal forms. In the orthodontics, the distance and the angle between the landmarks are calculated, and are used for classifying the patterns of the skeletal forms of patients and the positions of their teeth, and so forth, specifying problems, making various diagnoses such as treatment plans, and evaluating changes before and after treatment and changes by growth.
The cephalometrics films are generally taken by setting the standard of the head with a rod called Ear-rod applied to the right and left external auditory meatuses. However, they vary to some extent in the setting and are limited in accuracy. Further, they are radiographs for making the human body transparent. In the case of a lateral cephalogram, for example, right and left bones are overlapped with each other, so that a measuring area may, in some cases, be difficult to see.
In recent years, an image processing technique (computer software) capable of constructing tomographing data obtained by a tomograph called CT (Computed Tomography) or MRI (Magnetic Resonance Imaging) in three dimensions on a computer and observing a skull has been developed.
In the existing computer software, it is possible to construct a three-dimensional image (3D image) on a display on the basis of the multi-tomographing image data, freely rotate and move the 3D image on the display, and observe the 3D image at an arbitrary viewpoint.
It is also possible to arbitrarily set a portion (a range) to be cut, the position thereof, and the direction of the cutting on the display, and display an image on a cut plane.
In the current computer system and software, however, it is impossible to perform processing for setting reference planes using landmarks as a basis, displaying a three-dimensional image based on the set reference planes, and rotating the three-dimensional image on the basis of the set reference planes.
When an attempt to compare past data and current data relating to one patient is made, therefore, images to be displayed are not respectively images using anatomic landmarks as a basis but images displayed using reference axes which have been positioned at the time of radiographing as a basis. Moreover, the reference axes which have been positioned at the time of radiographing are set every time the radiographing is performed. Therefore, the two images to be compared do not conform to each other in the reference axes, so that both the images cannot be correctly compared with each other.
Similarly, even when the skeletal forms, for example, of a plurality of patients are compared with one another, each of the images is constructed as a three-dimensional image on the basis of the reference axes which have been positioned at the time of radiographing. Accordingly, a plurality of images cannot be compared with one another on the basis of the same reference axes.